These teachings relate generally to semi-active laser (SAL) receivers which are laser spot trackers used in expendable munitions such as laser-guided bombs.
Typical SAL receivers use an analog-to-digital converter (ADC) to continuously digitize the signal from each pixel at high speed to follow the short laser pulse return, and use digital processing to examine the waveform seen by each pixel for laser pulses of interest. This architecture limits the array size to about 2×2. Typical SAL receivers use 2×2 pixel “quadrant” photodetectors to provide information on the alignment of the SAL receiver and bomb relative to the laser spot. One problem with these systems is that the 2×2 pixel array limits the resolution and field of view (FOV) of the sensor. Some systems partially overcome this limitation by adding a gimbal (mechanical panning mechanism) but this adds significant cost to the SAL receiver, which must be inexpensive because they are used in expendable munitions. Existing SAL receivers cannot increase the array size to be much larger than 2×2 because they use an analog-to-digital converter (ADC) to continuously digitize the signal from each pixel at high speed (typically around 100 MHz) to follow the short laser pulse return, and use digital processing to examine the waveform seen by each pixel for laser pulses of interest. Using a larger array size, 32×32=1024 pixels for example, would require 1024 ADC circuits and 1024 digital signal processing channels which would be prohibitive in terms of power, size, and cost.
An additional problem with existing SAL systems are that they use a 1.06 micron laser wavelength, which causes eye damage and is not covert since most current EO sensors including image intensifiers can see this wavelength and thus determine the location of the laser designator. Furthermore, existing SAL systems can experience significant performance degradation when the sun is in the FOV of the sensor.
There is a need for SAL receiver designs that can use large focal plane arrays without exceeding the cost and size limitations
There is a further for SAL receiver designs that can enable the use of eye safe lasers.